How do you handle errors in an RxJS stream?

Answer

Handle expected errors inside the pipeline with catchError, return an appropriate fallback or rethrow, and keep error state visible to the UI. An unhandled error terminates the subscription, so decide whether the stream should recover.

Context

RxJS models asynchronous values as composable streams. The important design choice is the source lifetime and concurrency rule: cancel, merge, queue, or ignore competing work deliberately.

Example

const results$ = query$.pipe(
  debounceTime(250),
  distinctUntilChanged(),
  switchMap(query => api.search(query))
)

switchMap ensures an older search result cannot overwrite a newer query.

Practical considerations

1. Choose the approach from the requirement and constraints, not from habit.
2. Include validation, error handling, and cleanup where the boundary requires them.
3. Verify the observable result with focused tests or measurement.

Follow-up prompts

• What failure mode would you expect if this were implemented incorrectly?
• How would you test this behaviour?
• What changes when the feature must scale to a larger application or team?

In practice

For this easy-level topic, make assumptions explicit, choose the smallest safe implementation, and verify the behavior at the relevant boundary.